title: Simultaneous orientation contrast for lines in the human fovea.
abstract: When it is surrounded by lines of a differing orientation, a test line changes its apparent orientation in a direction away from that of the surround lines. Using a nulling technique to arrive at numerical values, the properties of this simultaneous orientation contrast have been analyzed: it diminishes with distance of the surround lines; rises and then falls off as a function of surround line orientation; decreases with exposure duration; is sharply tuned (+/- 100 msec) for synchrony of test and surround line presentation; is robust to differences between test and surround line disparity but not intensity; and is reduced with dichoptic presentation of test and surround lines. Orientation contrast can be induced in a variety of oriented features, including illusory contours, an ellipse, a moving dot and a row of dots or lines, but two dots alone don't suffice. The results are taken as evidence that orientation is a domain sui generis, in which simultaneous contrast is exhibited in the same manner as in the domains of color, brightness and disparity.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors.forename: G
authors.initials: G
authors.lastname: Westheimer
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology*; D005403:Fixation, Ocular; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D009903:Optical Illusions / Q000502:physiology; D010364:Pattern Recognition, Visual / Q000502:physiology; D012399:Rotation; D013997:Time Factors